the Junkers Jumo 205 aircraft engine was
the most famous of a series of aircraft
diesel engines that were the first and
for more than half a century the only
successful aviation diesel power plants
the jumo 204 first entered service in
1932 later engines in the series were
stark jumo 206 Juneau 207 and jumo 208
and differed in stroke and poor and
super charging arrangements in all more
than 900 of these engines were produced
in the 1930s and through most of world
war ii design and development
these engines all used a two-stroke
cycle with 12 Pistons sharing six
cylinders piston crown two piston crown
in an opposed piston configuration this
unusual configuration required two
crankshafts one at the bottom of the
cylinder block and the other at the top
geared together
the Pistons move towards each other
during the operating cycle intake and
exhaust manifolds were duplicated on
both sides of the block there were two
cam operated injection pumps per
cylinder each feeding two nozzles for
four nozzles per cylinder in all as is
typical of two-stroke designs the Zhu
Mo's used fixed intake and exhaust port
apertures cut into the cylinder liners
instead of valves during their
manufacture which were uncovered when
the Pistons reached a certain point in
their stroke normally such designs have
poor volumetric efficiency because both
ports open and close at the same time
and are generally located across from
each other in the cylinder this leads to
poor scavenging of the burn charge which
is why valve less two-strokes generally
produce smoke and are inefficient the
jumo solved this problem to a very large
degree through clever arrangement of the
ports the intake port was located under
the lower piston while the exhaust port
was under the upper the lower crankshaft
ran 11 degrees behind the upper meaning
that the exhaust ports opened and even
more importantly closed first allowing
proper scavenging this system made the
two-stroke jus Mo's run as cleanliness
as efficiently as full stroke engines
using valves but with consid
less complexity there is some downside
to the system as well for one since
matching Pistons were not closing at
quite the same time but one ran ahead of
the other the engine could not run as
smoothly as a true opposed style engine
in addition the power from the two
opposing crank shafts had to be geared
together adding weight and complexity a
problem the design shared with h-block
engines in the jumo these problems were
avoided to some degree by taking power
primarily from the upper shaft somewhat
offset upwards on the engines front end
all of the accessories such as fuel
pumps injectors and the scavenging
compressor were run from the lower shaft
meaning over half of its power was
already used up what was left over was
then geared to the upper shaft which
round the engines propeller in all about
three-quarters of the power to the
engines propeller came from the upper
crankshaft in theory the flat layout of
the engine could have allowed it to be
installed inside the thick wings of
larger aircraft such as airliners and
bombers details of the oil scavenging
system suggest this was not possible in
the engine had to be run as it was on
all designs using it variants a 12
cylinder version the jumo 218 was
designed but never built while a single
24 cylinder full crankshaft Junkers Jumo
223 was built and tested the jumo 204
and 205 were licensed to Napier and Sun
who built a small number as the Napier
cover in just prior to the wall after
the war they mounted three coverings in
a triangle layout to produce the Napier
Deltic which was for some time one of
the most powerful and compact diesel
engines in the world work on this engine
started in 1947 and engines were running
by 1950 applications the Jumo 205
powered early versions of the Junkers
jouer t6 bomber but was found to
unresponsive for combat and liable to
failure at maximum power common for
combat aircraft later versions of the
design also used the engine for extreme
high-altitude use
with the Jew 86 P and aversions for
high-altitude reconnaissance over the
British Isles it was far more successful
as a power unit for airships for which
its characteristics were ideal and for
non-combat applications such as the
block Minh Voss ha 139 airliner it's
more fuel efficient operation lent
itself the use on Germany's few maritime
patrol flying boat designs during world
war ii such as the bv 138 and BV 222
equals applications list equals Lachman
Voss BV 138 Lachman Voss ha 139 Lachman
Voss BV 222 dawnia do 18 dornier do 26
Junkers do 80 6 specifications data from
equals general characteristics equals
type six-cylinder 12 piston liquid
cooled opposed piston in-line two-stroke
diesel engine bore 105 millimetres
stroke 160 millimeters displacement 16.6
3 L length 76.5 inches width 21.5 4 in
height 52 point 1 7 in dry weight 595
kilograms equals components equals
supercharger spar 1/4 l GE BL a currency
say fuel system fuel injection fuel type
diesel oil system forced with one
pressure and to scavenge pumps cooling
system liquid cooled equals performance
equals power output 880 picoseconds at
2,800 RPM specific power 39.0 kilowatts
per liter compression ratio 17 1
power-to-weight ratio one point zero
nine kilowatts per kilogram other
notable opposed piston engines kamati s3
the common aqua commercial vehicle
engine Leyland Motors L 60 tank engine
used in the chieftain tank similar in
layout to the Junkers Jumo 205 and
Napier culverin rolls-royce k-6
engine smaller and improved version of
the L 60 used in the FP for 30 series
armored fighting vehicles and Swedish
tank strv 103 Napier Deltic Soviet
engine 5 TDF Houston tank T 64 Soviet
engine 6 TD Houston tanks t-80ud 284 and
al Khaled fairbanks-morse 38 8 and 1/8
see also list of aircraft engines
references equals notes equals equals
bibliography equals external links multi
crankshaft supposed piston engines
description and cutaway view Royal Air
Force Museum Jumo 205 opposed piston
engines coms Jumo 205 page opposed
piston engines coms jumo 207 page